I. Field of the Invention
The present invention relates to the field of the treatment of hot gases, particularly combustion gases, in order to recover, on the one hand, the heat conveyed by these gases and, on the other, the condensable materials present therein. It relates more particularly to the treatment of gas containing dust and/or condensable substances, which may in particular be produced in a furnace, such as a furnace for melting glass or similar mineral material.
II. Description of Related Art
In a glass furnace, the glass batch material is heated to the molten state at a temperature of about 1200 to 1300° C. using heat energy provided in particular by gas burners. The combustion gases escape from the furnace at a temperature of about 1000 to 1200° C., entraining a certain quantity of gaseous materials deriving from volatile components of the glass batch, such as boron.
The furnace gas exit zone is generally equipped with a cooling tower for recovering part of the heat of the combustion gases, for reuse to heat the primary combustion air, and also to condense the volatile materials in order to separate them and discharge the cooled gas to the atmosphere.
The cooling tower generally comprises a first stage in which the cold fluid is atmospheric air, which issues from the heat exchanger at a temperature of about 600° C. and can be recycled to the burners as oxidizing air, a stage in which the combustion gases treated issue at a temperature of about 700° C., and a second stage in which the cold fluid is water sprayed directly into the treated combustion gases, causing the solidification into dust of the condensable substances. The mixture of cooled gas, steam and dust is then separated by an electrostatic filter which traps the dust and discharges a gas at a temperature of about 400° C.
This discharge to the atmosphere represents a substantial loss of energy that may amount to several megawatt.hours of operation of an industrial glass production installation.
However, the presence of condensable materials, which represents several grams of material per cubic meter of hot gas, precludes the treatment of this gas in a conventional heat exchanger, because it would be very rapidly clogged by the condensed dust. It would only be capable of operating in short cycles interrupted by cleaning cycles which raise real intrinsic technical difficulties and which are also liable to disturb the production of glass.
In fact, the discharge to the atmosphere of condensable material is due to be prohibited shortly by environmental legislation. It is therefore becoming necessary for the flue gases to be stripped of condensable material before discharge.